Various techniques such as a technique using a reference light, and a stereo ranging technique using a plurality of cameras, are known as imaging techniques for obtaining a distance to a subject in a depth direction, in a format of two-dimensional array information. In recent years, imaging devices capable of obtaining distance information at relatively low costs have been increasingly needed to serve as newly developed input devices for consumer market.
In order to meet the needs, an imaging device with an imaging lens and a compound eye structure is proposed, which obtains images with multiple parallaxes, and prevents the degradation of resolution. The imaging device includes, for example, an imaging lens, and a plurality of optical systems serving as re-imaging optical systems arranged between the imaging lens and an imaging element. For example, a microlens array including a plurality of microlenses arranged on a flat substrate is used as the optical systems. Pixels are arranged below the microlenses, each on a position corresponding to a microlens, to obtain images through the microlenses. An image formed by the imaging lens is re-imaged on the imaging element by means of the re-imaging microlenses. The viewpoint of each individual image that is re-imaged is shifted from that of an adjacent image by the parallax according to the position of the corresponding microlens.
A distance to a subject can be estimated based on a triangulation method by image-processing the parallax images obtained from the microlenses. Furthermore, the parallax images can be combined and reconstructed as a two-dimensional image by image-processing.
Generally, the resolution of a two-dimensional image that is reconstructed from images of re-imaging optical systems is lower than that of a two-dimensional image without using the optical systems. Substantially switching whether a plurality of optical systems is used or not using a variable microlens array would lead to the switching of imaging modes; an imaging mode for obtaining a distance to a subject in depth direction and an imaging mode for obtaining a high-resolution two-dimensional image. A technique of switching the state of a liquid crystal optical device between an imaging state and a non-imaging state by applying or eliminating a voltage has been developed, in which the liquid crystal optical device including a combination of a liquid crystal lens element and a polarization controlling optical element serving as the aforementioned optical systems. However, the combination of two liquid crystal elements increases the number of components, and the thickness of the device.
Another technique is known, for deflecting the directions of light rays upward, downward, leftward, and rightward using a liquid crystal optical device including a first liquid crystal polarization element for polarizing light rays to one direction, a second liquid crystal polarization element for polarizing light rays to a direction perpendicular to the above one direction, and a liquid crystal polarization rotation element located between the first liquid crystal polarization element and the second liquid crystal polarization element. This liquid crystal optical device includes three liquid crystal optical elements that are stacked. This makes it difficult to decrease the thickness of the device.